Method for developing a resist pattern

Abstract: A photoresist pattern developed on a semiconductor substrate is rinsed by rinsing liquid. At this rinsing step, the rinsing liquid is heated to be decreased in surface tension, so that the collapse of the photoresist pattern is avoided.

Description: This invention relates to a method for developing a resist pattern, and more particularly to, a method for avoiding the collapse of a developed resist pattern at the time of rinsing the surface of the resist pattern. In the process of fabricating a semiconductor device, a predetermined pattern is transferred to or drawn on a resist film having a thickness of approximately 1µm or more appropriately covering the surface of a semiconductor substrate usually having minute unevenness thereon. Then, the semiconductor substrate is processed by, for instance, adopting photolithography using the resist pattern thus obtained as a protective mask pattern. In accordance with the conventional photolithography technology, it is very difficult that a sufficient focal depth is obtained to resolve a fine pattern of approximately 0.3µm or less with a predetermined precision, even if a wavelength of light for transferring a mask pattern to a semiconductor substrate is shortened, and a numerical aperture of a reducing projection lens is optimized. For this reason, there is necessity to adopt a technology such as X-ray lithography, etc. having a high resolution and a large focal depth. In case where a resist film exposed to a pattern by the X-ray lithography is developed, an ordinary resist film coating and developing apparatus is used. The apparatus is provided with a mount for a semiconductor substrate which is rotated by a motor. In the apparatus, a semiconductor substrate covered with a resist film is fixed on the mount by a vacuum chuck provided thereon. Then, developer is supplied on the resist film which is rotated along with the substrate fixed to the mount by the motor, so that a predetermined pattern is developed on the resist film. Subsequently, the developed resist film is rinsed on the mount in accordance with the supply of pure water, alcohol, etc. thereto under the situation where it is rotated along with the substrate by the motor. Finally, the resist pattern thus developed is dried on the mount. Such a conventional developing apparatus is described in the Japanese Utility Model Kokai No. 63-197331. The developing apparatus comprises a spin head having a spiral pipe therein for flowing liquid therethrough. In the developing apparatus, the liquid of a predetermined temperature is flown through the spiral pipe, so that the temperature distribution of developer supplied on a resist film is uniform to enhance the resist pattern precision. In the conventional developing apparatus, however, there is a disadvantage in that a resist pattern is collapsed due to surface tension of rinsing liquid flown into minute interstices of the developed resist pattern at the stage of rinsing the developed resist pattern, especially, when an aspect ratio which is a ratio between dimensions of longitudinal and transverse sides of the pattern becomes large, despite that any kind of a resist film is used. This disadvantage is observed even in case where the X-ray lithography providing a predetermined precision in the transfer of a super-minute pattern is used. A method for developing a photoresist pattern according to the preamble of claim 1 is disclosed in EP-A-0224273. In this method so called chemical liquids including a pretreatment liquid, a developer and a post-treatment liquid are heated before applied to a semiconductor substrate, and the aim of this known method is to improve the temperature control during the process such that it is independent from the ambient temperature and in the range of 5°C to 40°C with a tolerance of ± 0,1°C such that it is ensured that all wafers are developed at accurately the same temperature. Patents Abstract of Japan, vol. 12, No. 162 (E 609) and JP-62-274720 discloses a mechanism to heat a developer and a rinse liquid, in order to prevent decrease of reaction speed of resist on the substrate caused by the heat of vaporization of a treatment liquid sprayed on the substrate. From US-A-5223377 it is known to interrupt a developing step and to subject the photoresist to a heat treatment and then completing the development process, wherein the temperature during this interrupting process is in the range of about 30°C to 90°C. DE-A-4306033 discloses that it is advantageous to add a surface active agens to the rinse liquid in order to reduce the surface tension of the rinse liquid. In order to shorten the developing time and to improve reproducability of development Patents Abstracts of Japan, vol. 7, No. 206 (P-222) (1351) and JP-A-58102942 propose to heat the developer and/or a substrate. It is an object of the invention to provide a method for developing a resist pattern in which the collapse of the resist pattern is avoided. In the invention, the rinsing liquid is water and/or alcohol, and the semiconductor substrate is heated to be a predetermined temperature, so that the rinsing liquid is heated to the boiling point thereof or less by several degrees. Thus, the rinsing liquid is relieved in surface tension at the rinsing step, and the evaporation of the rinsing liquid is accelerated out of the semiconductor substrate in cooperation with the spin effect generated by the rotation of a semiconductor substrate holder. The invention will be explained in more detail in conjunction with appended drawings, wherein: Fig. 1 is an explanatory view explaining a method for developing a photoresist pattern in a first preferred embodiment according to the invention; Fig. 2A to 2E are schematic cross sectional views explaining the collapse of a photoresist pattern; and Fig. 3, 4A and 4B, and 5 are explanatory views explaining a method for developing a photoresist pattern in second to fourth preferred embodiments according to the invention. Fig. 1 shows a resist pattern developing apparatus in which a method for developing a resist pattern in the first preferred embodiment according to the invention is carried out. The resist pattern developing apparatus comprises a holder (or mount) 12 for holding a semiconductor substrate 11 coated with a resist film (not shown) to be developed, a vacuum chuck 21 for holding the semiconductor substrate 11 to be fixed on the holder 12 by vacuum, a heater 13 buried in the holder 12 for heating the semiconductor substrate 11 to be maintained at 50 to 100°C, a power supply 28 for applying a voltage to the heater 13, a thermo-sensor 22 for sensing the temperature of the holder 12 (and the semiconductor substrate 11), a reservoir 18 for containing developer 14, a pipe 26 for supplying the developer 14 to the resist film on the semiconductor substrate 11 by using a pump (not shown), a reservoir 19 for containing thermal medium (water or oil) 20, a reservoir 25 for containing rinsing liquid (pure water, alcohol, etc.) 15, a heater 17 for heating the thermal medium 20 to transfer the heat to the rinsing liquid 15, a power supply 16 for applying a voltage to the heater 17, a thermal-sensor 23 for sensing a temperature of the thermal medium 20, a pipe 27 for supplying the rinsing liquid 15 to a developed resist pattern, and control unit for controlling the power supplies 16 and 28 to be turned on and off by receiving sensor signals of the thermo-sensors 22 and 23. In operation, the semiconductor substrate 11 having the resist film is fixed on the holder 12 by the vacuum chuck 21 using vacuum, and the holder 12 is rotated together with the semiconductor substrate 11 by a motor (not shown). In this situation, the power supply 28 is turned on to activate the heater 13 by the control unit 24 receiving a temperature signal from the thermo-sensor 22, so that the semiconductor substrate 11 is heated to be maintained at 50 to 100° C. Then, the developer 14 is supplied through the pipe 26 on the surface of the resist film on the semiconductor substrate 11. Thus, the resist film is developed in accordance with a pattern transferred in advance thereon. At the same time, the power supply 16 is turned on to activate the heater 17, so that the thermal medium 20 is heated to transfer the heat to the rinsing liquid 15. Subsequently to the development of the resist film on the semiconductor substrate 11, the developed resist pattern is rinsed by the heated rinsing liquid 15. The rinsing liquid 15 is relieved in surface tension by the temperature increase based on the heating thereof, so that the rinsing liquid 16 is well flown into the minute interstices of the resist pattern by reduced surface tension. Consequently, the collapse of the resist pattern is effectively avoided, even if it is extremely minute. Figs. 2A to 2E show the rinsing liquid 15 supplied on the photoresist pattern 40 on the semiconductor substrate 11 (not shown in Figs. 2A to 2E, but in Fig. 1). The rinsing liquid 15 is evaporated to be thinner as a liquid layer, especially, as shown in Figs. 2C to 2E, and the photoresist pattern 40 may be collapsed due to the surface tension of the rinsing liquid 15 in an interstice of the photoresist pattern 40, unless the rinsing liquid 15 is heated as in the conventional method for developing a photoresist pattern. The surface tension of the rinsing liquid 15 remarkably affects the photoresist patten 40, when the liquid layer is approximately equal to the height of the photoresist pattern 40 to be exposed at the top thereof to the outer atmosphere, as shown in Fig. 2C. Then, the collapse of the photoresist pattern 40 may start, and adjacent layers become contacted, as shown in Fig. 2E. On the contrary, the collapse of the photoresist pattern 40 is avoided in the invention, because the surface tension of the rinsing liquid 15 is reduced in accordance with the heating of the rinsing liquid 15. Fig. 3 shows an apparatus for developing a photoresist pattern used for a method for developing a photoresist pattern in the second preferred embodiment according to the invention, wherein like parts are indicated by like reference numerals as used in Fig. 1, and the control unit 24, etc. are not shown for simple illustration. In the apparatus, an infrared ray lamp 31 is provided to heat the semiconductor substrate 11 at the rinsing step, so that the rinsing liquid 15 is effectually heated on the semiconductor substrate 11. This apparatus is advantageously used in case where a number of semiconductor substrates are continuously processed, because each semiconductor substrate is suppressed in temperature increase at the developing step. Figs. 4A and 4B show an apparatus used for a method for developing a photoresist pattern in the third preferred embodiment according to the invention, wherein like parts are indicated by like reference numerals as used in Figs. 1 and 3. In the apparatus, a semiconductor substrate holder 12A having a vacuum chuck 21A is used at the developing step, and a semiconductor substrate holder 12B is used at the rinsing step. As apparent from the illustration of Figs. 4A and 4B, the developing of a photoresist pattern, and the rinsing thereof are carried out on the different holders 12A and 12B. Consequently, the semiconductor substrate 11 is suppressed in temperature increase at the developing step, even if a number of semiconductor substrates are continuously processed. On the contrary, the rinsing liquid 15 and the semiconductor substrate 11 are heated to be increased in temperature at the rinsing step. Fig. 5 shows an apparatus used for a method for developing a photoresist pattern in the fourth preferred embodiment according to the invention, wherein like parts are indicated by like reference numerals as used in Figs. 1, 3, 4A and 4B. The apparatus comprises a water vapor (steam) supply mechanism which comprises a heater 52 energized by a power supply 51, a reservoir 53 for containing thermal medium 54 to be heated by the heater 52, a reservoir 55 for containing pure water 56 to be heated by the thermal medium 54, and a pipe 57 for transporting steam to be supplied on a developed photoresist from nozzles 58 provided at the end thereof. In the fourth preferred embodiment, the effect of relieving the surface tension of the rinsing liquid 15 is more enhanced by supplying the steam from the nozzles 58 on the developed photoresist pattern and by heating the rinsing liquid 15 and the semiconductor substrate 11 by the heaters 13 and 17.

Claims: A method for developing a photoresist pattern, comprising the steps of: coating a photoresist film on a semiconductor substrate (11); exposing said photoresist film on said semiconductor substrate (11) to a predetermined pattern; supplying developer (14) on said photoresist film on said semiconductor substrate (11) to develop said photoresist pattern; supplying a heated rinsing liquid (15) on said photoresist pattern developed on said semiconductor substrate (11) to rinse said photoresist pattern, characterized in that the surface of said semiconductor substrate (11) having said photoresist pattern thereon is heated during said rinsing liquid supplying step to a predetermined temperature such that rinsing liquid is at the boiling point thereof or several degrees less. A method for developing a photoresist pattern according to claim 1 wherein: said surface of said semiconductor substrate (11) is heated to said predetermined temperature by heating a holder (12) on which said semiconductor substrate (11) is supported. A method for developing a photoresist pattern according to claim 1 wherein: said rinsing liquid is water and/or alcohol and said predetermined temperature is a temperature to heat said rinsing liquid to the boiling point thereof. A method for developing a photoresist pattern according to claim 1 wherein: said semiconductor substrate is fixed on a first semiconductor substrate holder (12A) at said developer supplying step, and on a second semicondcutor substrate holder (12B) at said rinsing liquid supplying step. A method for developing a photoresist pattern according to claim 1 wherein: said surface of said semiconductor substrate is heated to said predetermined temperature by an infrared ray lamp (31). A method for developing a photoresist pattern according to claim 1 wherein said heating of said surface is effected by supplying steam on said photoresist pattern developed on said semiconductor substrate (11) at said rinsing liquid supplying step.

Inventors: SUZUKI KATSUMI, SUZUKI, KATSUMI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1994
Main classification: G03F7
IPC codes: G03F7